Optical information recording medium

ABSTRACT

An optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs by using a material having optimum optical characteristics as an organic dye material of a recording layer. The optical information recording medium comprises a recording layer on a transparent substrate having a spiral pregroove formed thereon, wherein the track pitch Tp of the pregroove is 1.0 μm≦Tp≦1.2 μm and the optical phase difference ΔS is 0.15≦ΔS≦0.55.

TECHNICAL FIELD

[0001] The present invention relates to an optical information recording medium of once type such as a CD-R (Compact Disc-Recordable), and more particularly to an optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs.

BACKGROUND ART

[0002] Generally, a CD-R is known as an optical information recording medium of write-once type which is reproduced by a CD (Compact Disc) drive or a CD-ROM (Compact Disc Read Only Memory) drive.

[0003] The optical recording medium such as a CD-R has a basic structure in which a recording layer having an organic dye film is formed on a transparent substrate having a spiral pregroove, a reflecting layer of a metallic film is formed thereon, and further a protective layer of an ultraviolet curing resin is formed thereon, and is configured to record by irradiating a laser beam from the side of the transparent substrate to the recording layer to partly decompose the dye of the recording layer.

[0004] This optical information recording medium is expanding its market rapidly because of merits such as compatibility with CDs and a unit cost per bit lower than that of paper, and recording apparatuses, which can write at a recording speed ten times or more higher than an ordinary speed, and corresponding media are being supplied to the market in response to needs for high-speed processing.

[0005] Furthermore, it is demanded on the market that a high capacity is provided in correspondence with an increasing amount of data processing every year, and it is assumed that a capacity of 1.3 GB (Giga Bytes) or more is required for an amount of data for image processing or the like.

[0006] When the above pits are recorded by means of a laser beam having a wavelength of 780 nm, NA (Numerical Aperture) of 0.45 to 0.50 and a spot diameter of about 1.6 μm employed in the current CD-ROM/-R/-RW drives in order to secure a recording amount of about two times of the currently used ones without changing an outer diameter of conventional optical information recording media of write once type, there are problems as described below.

[0007] Specifically, when a tracking pitch is simply changed to have a smaller interval, unwanted signals are taken from an adjacent track when reproducing, namely so-called crosstalk increases, and a clear signal cannot be obtained, resulting in increase of so-called jitter which is the variation in the pit signal at the time of reproduction.

[0008] When the recording pits are merely configured to be formed in high density in a linear velocity direction, an effect of heat generated when the pits are formed causes a phenomenon which is called heat interference affecting on the recording state of the next pit, a length of the previously recorded pit and an interval to the next pit become short, so that a position of the next written pit is easily displaced. As a result, a jitter increases. This phenomenon is also seen when recording at a high speed.

DISCLOSURE OF THE INVENTION

[0009] It is an object of the present invention to provide an optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs by using a material having optimum optical characteristics as an organic dye of a recording layer.

[0010] In the optical information recording medium of the present invention, the pregroove has a track pitch Tp of 1.0 μm≦Tp≦1.2 μm; and when it is assumed that the pregroove has a depth Dsub, the pregroove portion on the interface between the reflecting layer and the recording layer has a displacement depth Dabs, a real part of a complex index of refraction of the recording layer is nabs, a real part of a complex index of refraction of the transparent substrate is nsub, and a wavelength of a reproduction light is λ, an optical phase difference ΔS=2Dsub{nsub-nabs(1−Dabs/Dsub)}/λ is 0.15≦ΔS≦0.55. Here, nabs and nsub are values for λ. Details of ΔS are disclosed in Japanese Patent Laid-Open Publication No. 2-24542.

[0011] When the optical phase difference ΔS is less than 0.15, a sufficient tracking error signal required at the time of recording is hardly obtained, and when it exceeds 0.55, it is difficult to reproduce stably because a maximum reflectance of a reproduction signal becomes low.

[0012] Here, it is preferable that a thickness Dg of the recording layer on the pregroove portions is 80 nm≦Dg≦120 nm.

[0013] It is preferable that an optical distance difference ΔnDg between the reflected light via the pregroove and the reflected light via the land between the pregroove portions after the recordation of information on the recording layer is 40 nm≦ΔnDg≦60 nm.

[0014] In this case, the thickness Dg of the recording layer on the pregroove portions is preferably 80 nm≦Dg≦120 nm.

[0015] It is preferable that an average decomposition rate Ad of the organic dye material for the recording layer is Ad≦7.5%. Here, the average decomposition rate Ad in the entire dye is an average decomposition rate to the entire dye in the recording layer.

[0016] Recording of information on the optical information recording medium according to the present invention is performed by forming so-called pits by partly changing optical characteristics of the recording layer in the pregroove, e.g., by heating the dye material in the organic dye film configuring the recording layer with a laser beam to partly change (decompose) its structure.

[0017] And, the decomposition of the dye when recording and the modulated degree of the signal as a result are proportional to the optical distance difference ΔnDg produced between the recorded portion and the non-recorded portion.

[0018] Here, the thickness Dg of the recording layer on the pregroove is preferably thinner in order to decrease an effect of heat interference. Therefore, it is practically preferable that a difference Δn of the refractive index between the recorded portion and the non-recorded portion is larger.

[0019] The difference Δn of the refractive index between the recorded portion and the non-recorded portion becomes approximately n=1.6 in the same way as a usual resin material when the dye is 100% decomposed, so that it depends on the refractive index of the dye layer when not recorded and the decomposition rate of the dye in the recording pits. Here, Δn is a value at a reproduction wavelength.

[0020] Therefore, it is desired that the average decomposition rate Ad of the entire dye on the recorded substrate exceeds 7.5%. In this state, a sufficient degree of modulation and a low jitter value can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a perspective diagram partly broken away of a general structure of an optical information recording medium according to the present invention.

[0022]FIG. 2 is an enlarged sectional diagram showing the essential part of the optical information recording medium shown in FIG. 1.

[0023]FIG. 3 is a diagram showing a relation between ΔS and a tracking error.

[0024]FIG. 4 is a diagram showing a relation between ΔS and a reflectance.

[0025]FIG. 5 is a diagram showing a relation between ΔS and BLER.

[0026]FIG. 6 is a diagram showing a relation between k and BLER.

[0027]FIG. 7 is an enlarged sectional diagram showing the essential part of FIG. 1.

[0028]FIG. 8 is a diagram showing a general formula of benzoic cyanine dye.

[0029]FIG. 9 is a diagram showing a general formula of aluminium salt.

BEST MODE FOR CARRYING OUT THE INVENTION

[0030] Modes of implementation of the optical information recording medium according to the present invention will be described in detail with reference to the accompanying drawings.

[0031]FIG. 1 is a perspective diagram partly broken away of a general structure of an optical information recording medium according to the present invention, and FIG. 2 is an enlarged sectional diagram showing an essential part of the optical information recording medium shown in FIG. 1.

[0032] In FIG. 2, the sectional diagram of the optical information recording medium of FIG. 1 taken in its radial direction is shown, wherein block 200-1 shows an enlarged view of a groove section and a land section, and block 200-2 shows an enlarged view of the groove section.

[0033] In FIG. 1 and FIG. 2, an optical information recording medium 100 is formed by forming a recording layer 102, which is formed of an organic dye film, on a transparent substrate 101 by a film-forming method, e.g., a spin-coating method or the like, and forming a reflecting layer 103 on the recording layer 102 by a sputtering method, a vapor deposition method or a plasma CVD (Chemical Vapor Deposition) method, and forming a protective layer 104 on the reflecting layer 103.

[0034] Here, a spiral pregroove 201 is formed on the transparent substrate 101 and can be formed by an injection forming method, which injection-forms the spiral pregroove 201 by means of a stamper. The spiral pregroove 201 may be formed by another forming method other than the stamper.

[0035] A material for the transparent substrate 101 can be any kind of material which has high permeability to light having a wavelength of the laser beam used for recording and reproducing of information on and from the optical information recording medium 100 and is not deformed considerably by an external force, an environmental change, or the like, and polycarbonate can be used for example.

[0036] The organic dye film forming the recording layer 102 can be a dye material alone or one containing a prescribed amount of a stabilizing material in order to improve environmental stability.

[0037] The dye material includes those which have a high refractive index and an appropriate absorption coefficient in the vicinity of wavelength 770 nm to 830 nm of the laser beam used to record and reproduce information on and from the optical information recording medium 100. For example, cyanine dye, metal-containing phthalocyanine dye, metal-containing azo dye or the like can be used. As the optical information recording medium 100 of this mode of implementation, it is desirable to use benzoindodicarbo cyanine dye as the aforementioned dye material.

[0038] The reflecting layer 103 is a metallic film which mainly contains Au, Ag, Cu, Pd, Al, or an alloy of them and also a prescribed amount of other elements.

[0039] In the optical information recording medium 100 of this mode of implementation, in order to realize a recording capacity of 1.3 GB or more without changing the outer diameter of currently-used CD-Rs, a track pitch Tp is set to a range of 1.0 μm≦Tp≦1.2 μm, and the pregroove 201 is formed on the transparent substrate 101 of the optical information recording medium 100 in such a way to meet the track pitch Tp.

[0040] Here, the track pitch Tp is determined by an interval between the adjacent pregrooves 201, namely a distance between the centers of the adjacent pregrooves 201 as shown in FIG. 2.

[0041] When the track pitch Tp is less than 1.0 μm, jitter becomes 35 ns or more due to an effect of crosstalk, and the stable recording-reproducing properties can not be obtained. Jitter of less than 35 ns is a value specified by the CD-R Standard, Orange Book Ver. 2.0.

[0042] When the track pitch Tp exceeds 1.2 μm, a linear velocity of 0.77 m/s or more is required on the side of a recording device in order to achieve a capacity of about 1.3 GB, and the stable recording-reproducing properties can not be obtained due to heat interference.

[0043] Here, for the optical information recording medium 100 having the aforementioned track pitch, optical designing of the recording layer 102 formed on the transparent substrate 101 is significant.

[0044] Optical phase difference ΔS of the land-groove section in a non-recorded state is desired to be in a range of 0.15≦ΔS≦0.55. A relation between ΔS and disc properties is described below. The ΔS is highly correlated with the tracking error signal and reflectance when recording or reproducing. According to the test results shown in FIG. 3, a tracking error signal is small and it is difficult to record stably in an area of ΔS>0.15. As shown in FIG. 4, when Δ>0.55, enough reflectance cannot be obtained, and reproduction cannot be made stably after recording. Therefore, stable recording and playback can be made with a low BLER (block error rate) in a range of 0.15≦S≦50.55 as shown in FIG. 5.

[0045] Here, when it is assumed that a depth of the pregroove 201 shown in FIG. 2 is Dsub, a displacement depth of an interface between the reflecting layer 103 and the recording layer 102 at the pregroove 201 section is Dabs, the real part of the complex index of refraction of the recording layer 102 in the pregroove 201 portion is nabs, the real part of the complex index of refraction of the transparent substrate 101 is nsub, and a wavelength of reproduction light is Δ, the optical phase difference ΔS is ΔS=2Dsub{nsub-nabs(1-Dabs/Dsub)}/λ.

[0046] Thickness Dg of the recording layer on the pregroove portions is desirably 80 nm≦Dg≦120 nm. When Dg is less than 80 nm, a sufficient degree of modulation (55% or more in provisional standards) is hardly obtained, and as a result, jitter (the fluctuation) becomes worse, and the stable reproduction cannot be made. If Dg exceeds 120 nm, jitter becomes worsen due to an effect of heat interference, and stable reproduction cannot be made.

[0047] Incidentally, the decomposition of the dye of the recording layer 102 when recording and the degree of modulation of the signal as a result are proportional to an optical distance difference ΔnDg produced between the recorded section and the non-recorded section of the recording layer 102.

[0048] Here, Δn is a difference in refractive index (the real part of the optical constant) between the recorded section and the non-recorded section as shown in FIG. 2, and Dg is a thickness of the recording layer 102 on the pregroove 201.

[0049] In this mode of implementation, it is configured in such a way that the optical distance difference ΔnDg is 40 nm≦ΔnDg≦60 nm. Here, the thickness Dg of the recording layer 102 on the pregrooves 201 is preferably thinner in order to decrease the influence of the heat interference, and it is preferable that the difference Δn of refractive index between the recorded section and the non-recorded section is larger in practice.

[0050] When ΔnDg (nm) is less than 40 nm, a sufficient degree of modulation (55% or more in provisional standards) is hardly obtained, and as a result, jitter becomes worsen, and the stable reproduction cannot be made. When ΔnDg exceeds 60, jitter becomes worsen due to an effect of heat interference, and also stable reproduction cannot be made.

[0051] Because the difference Δn in refractive index between the recorded section and the non-recorded section becomes approximately n=1.6 similar to a common resin material when the dye is 100% decomposed, it depends on a refraction index of the dye layer when not recorded and a decomposition rate of the dye in the recorded pits. Therefore, it is desirable that an average in-pit decomposition rate Pd of the dye in recording pits exceeds 50% (see block 400-1 in FIG. 4), and an average decomposition rate Ad of the dye on the recorded substrate as the whole exceeds 7.5% (see block 400-1 in FIG. 4). Under such a condition, an enough degree of modulation and a low jitter value can be obtained.

[0052] And, imaginary part k of an optical constant relating to light absorption of the recording layer 102 is preferably 0.10≦k≦0.25, and if it is less than this range, enough photo absorption sensitivity for recording can not be obtained, and an enough modulation signal is hardly obtained. If the imaginary part k is out of the above range, an enough reflectance necessary for the reproduction cannot be obtained.

[0053] Therefore, stable recording or reproduction is not made on or of a recording medium having a light absorptive layer beyond the above range, and the BLER value increases when reproduced after recording as shown in FIG. 6. BLER of the stable reproduction value is 220 cps or less.

[0054]FIG. 3 is an enlarged sectional diagram of the essential part relating to the formation of pits on the optical information recording medium 100 shown in FIG. 1.

[0055] In FIG. 3, block 400-1 shows an enlarged state of the pits formed on the optical information recording medium 100. In the drawing, Pd denotes an average in-pit decomposition rate of the dye in each pit 401, and Ad denotes an average decomposition rate of the whole dye.

[0056] In this mode of implementation, a dye material and recording method, by which the average decomposition rate Ad of the dye becomes Ad≧7.5%, are used. If it is less than 7.5%, an enough degree of modulation cannot be obtained, the degree of modulation becomes small, and the jitter value becomes high. Thus, a stable reproduction characteristic is not obtained easily.

[0057] As an evaluation method, the absorbance of a solution of a decomposition disc dye layer is evaluated. The disc is decomposed, its dye layer is dissolved in a prescribed amount of solvent, and absorbance (Abs) of a spectrum peak of the solution is measured. Calculation is performed according to Ad=(1-(post-recording solution absorbance/pre-recording solution absorbance))×100.

[0058] Embodiment 1

[0059] A polycarbonate substrate having a thickness of 1.2 mm, an outer diameter of 120 mm and an inner diameter of 15 mm according to AFM measurement, on which a spiral pregroove having a width Dw of 0.43 μm, a depth Dsub of 175 nm and a pitch of 1.1 μm was formed, was produced by an injection molding method. And, 80 parts by weight of a dye which was a benzoic cyanine dye having the structural formula shown in FIG. 7 as a recording dye and 20 parts by weight of a near infrared absorptive dye which was aluminium salt having the structural formula shown in FIG. 8 as a light stabilizer, were dissolved in diacetone alcohol at 25 g/l. The obtained solution was applied on the aforementioned substrate to form a light absorptive layer having an average thickness Dav of 65 nm and an in-groove film thickness Dg of 106 nm. At this time, the groove depth Dabs on the dye film was 105 nm. The dye layer had the real part n of the optical constant of 2.6 and the imaginary part k of 0.12 at a wavelength of 780 run. Accordingly, when a laser wavelength was 780 nm, ΔS was 0.24. A light reflective layer with Ag of 80 nm was formed on the substrate having the dye film by RF sputtering, and an ultraviolet-curable resin (Dainippon Ink and Chemicals, Inc, SD-211) was spin coated as a protective layer on the reflecting layer, and the coated substrate was exposed to ultraviolet light to form a protective layer with a thickness of 6 μm. On the entire disc surface of the light recording medium thus produced, EFM signals were recorded at 3.6 m/s four times faster than its reproduction speed, by a recording apparatus (Pulse-tech, DDU-1000) using a laser beam of a wavelength of 784 nm, NA of 0.55 in such a way that the EFM signals could be obtained when reproduced at 0.9 m/s. And its reproduction was evaluated at 0.9 m/s. At that time, there were obtained good properties such as I11/Itop=0.65, 13/Itop=0.25, BLER 5.3 cps and RF jitter of 35 ns or less in all the signal range. Maximum reflectance Rtop of the signal after recording was 65%R. The real part of the optical constant on the recorded pit portions on the disc was 2.1 when evaluated and, therefore, Δn was 0.5 and ΔnDg was 53 nm. At that time, the average decomposition rate Pd in the pits was 50%, and the average decomposition rate of the dye film was 18%.

[0060] In the general formula of FIG. 7, Y is H, R is —(CH₂)₃—CH₃, and X⁻ is BF₄ ⁻ in this embodiment. In the general formula of FIG. 8, R is —(CH₂)₃—CH₃, and X⁻ is SbF₆ ⁻.

[0061] It is seen from the above embodiment that an optical information recording medium having good properties such as RF jitter and the like at high-density recording and sufficient characteristic margin can be provided.

[0062] Embodiment A

[0063] Using 80 parts by weight of the dye and 20 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 51 nm and an in-groove film thickness Dg of 82 nm was formed. At that time, a groove depth Dabs on the dye film was 118 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.12 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength was 780 nm, ΔS was 0.32. The others were same as in the first embodiment. The optical recording medium thus prepared was evaluated by the same method as in the first embodiment, and there were obtained good properties such as I11/Itop=0.65, 13/Itop=0.21, BLER 3.4 cps and RF jitter of less than 35 ns in the entire signal range. Maximum reflectance Rtop of the signal after recording was 62%R. The real part of the optical constant on the recorded pit portions on the disc was 2.1 when evaluated and, therefore, Δn was 0.5 and ΔnDg was 41 nm. At that time, the average decomposition rate Pd in the pits was 51%, and the average decomposition rate of the dye film was 12%.

COMPARATIVE EXAMPLE A

[0064] Using 80 parts by weight of the dye and 20 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 48 nm and an in-groove thickness Dg of 74 nm was formed. At that time, a groove depth Dabs on the dye film was 122 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.12 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength was 780 nm, ΔS was 0.36. The others were same as in the first embodiment.

[0065] Evaluation was performed by the same method as in the first embodiment, and there were obtained I11/Itop=0.52, 13/Itop=0.18, BLER 230 cps and RF jitter of 38 ns for 3T jitter. Thus, stable reproduction could not be made.

[0066] Maximum reflectance Rtop of the signal after recording was 64%R. The real part of the optical constant on the recorded pit portions on the disc was 2.1 when evaluated and, therefore, Δn was 0.55 and ΔnDg was 41 nm. At that time, the average decomposition rate Pd in the pits was 53%, and the average decomposition rate of the dye film was 13%.

COMPARATIVE EXAMPLE B

[0067] Using 70 parts by weight of the dye and 30 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 52 nm and an in-groove film thickness Dg of 84 nm was formed. At that time, a groove depth Dabs on the dye film was 110 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.10 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength is 780 nm, ΔS was 0.28. The others were same as in the first embodiment. Evaluation was performed by the same method as in the first embodiment, and there were obtained I11/Itop=0.51, I3/Itop=0.17, BLER 310 cps and RF jitter of 41 ns for 3T jitter. Thus, stable reproduction could not be made. Maximum reflectance Rtop of the signal after recording was 68%R. The real part of the optical constant on the recorded pit portions on the disc was 2.3 when evaluated and, therefore, Δn was 0.4 and ΔnDg was 34 nm. At that time, the average decomposition rate Pd in the pits was 44%, and the average decomposition rate of the dye film was 13%.

[0068] Embodiment C

[0069] Using 80 parts by weight of the dye and 20 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 75 nm and an in-groove film thickness Dg of 116 nm was formed. At that time, a groove depth Dabs on the dye film was 94 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.12 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength was 780 nm, ΔS was 0.17. The others were same as in the first embodiment. Evaluation was performed by the same method as in the first embodiment, and there were obtained good properties such as I11/Itop=0.67, I3/Itop=0.28, BLER 50.2 cps and RF jitter of 35 ns or less for the entire signal range. Maximum reflectance Rtop of the signal after recording was 63%R. The real part of the optical constant on the recorded pit portions on the disc was 2.1 when evaluated and, therefore, Δn was 0.5 and ΔnDg was 58 nm. At that time, the average decomposition rate Pd in the pits was 55%, and the average decomposition rate of the dye film was 16%.

[0070] Comparative Example C

[0071] Using 80 parts by weight of the dye and 20 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 78 nm and an in-groove thickness Dg of 124 nm was formed. At that time, a groove depth Dabs on the dye film was 92 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.12 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength was 780 nm, ΔS was 0.16. The others were same as in the first embodiment. Evaluation was performed by the same method as in the, first embodiment, and there were obtained I11/Itop=0.69, I3/Itop=0.28, BLER 286 cps and RF jitter of 41 ns for 3T jitter. Thus, stable reproduction was difficult. Maximum reflectance Rtop of the signal after recording was 64%R. The real part of the optical constant on the recorded pit portions on the disc was 2.1 when evaluated and, therefore, Δn was 0.4 and ΔnDg was 50 nm. At that time, the average decomposition rate Pd in the pits was 48%, and the average decomposition rate of the dye film was 14%.

COMPARATIVE EXAMPLE D

[0072] Using 90 parts by weight of the dye and 10 parts by weight of the light stabilizer of the first embodiment, a light absorptive layer with an average thickness Dav of 75 nm and an in-groove thickness Dg of 117 nm was formed. At that time, groove depth Dabs on the dye film was 90 nm. The real part n of the optical constant was 2.6 and the imaginary part k was 0.14 when the dye layer had a wavelength of 780 nm. Accordingly, when it was assumed that the laser wavelength was 780 nm, ΔS was 0.18. The others were same as in the first embodiment. Evaluation was performed by the same method as in the first embodiment, and there were obtained I11/Itop=_(0.70,) I3/Itop=0.27, BLER 230 cps and RF jitter of 401 ns for 3T. Thus, stable reproduction was difficult. Maximum reflectance Rtop of the signal after recording was 65%R. The real part of the optical constant on the recorded pit portions on the disc was 2.0 when evaluated and, therefore, Δn was 0.55 and ΔDng was 0.55. At that time, the average decomposition rate Pd in the pits was 58%, and the average decomposition rate of the dye film was 19%.

[0073] Embodiment E

[0074] EFM signal was recorded at 3.6 m/s, which was four times faster than its reproduction speed, on the entire surface of the disc prepared in the first embodiment in such a way that the EFM signal can be obtained when reproduced at 0.9 m/s, by a recording apparatus (Pulse-tech, DDU-1000) at recording power of 7.5 mW, using a laser beam with wavelength of 784 nm and NA of 0.55, and its reproduction was evaluated at 0.9 m/s. There were obtained I11/Itop=0.56, I3/Itop=0.20, BLER 80 cps and RF jitter of 35 ns or less for the entire signal range. Thus, stable playback could be made. Maximum reflectance Rtop of the signal after recording was 65%R. At that time, the average decomposition rate of the dye film was 8.2%.

COMPARATIVE EXAMPLE E

[0075] EFM signal was recorded at 3.6 m/s, which was four times faster than its playback speed, on the entire surface of the disc prepared in the first embodiment in such a way that the EFM signal could be obtained when reproduced at 0.9 m/s, by a recording apparatus (Pulse-tech, DDU-1000) at recording power of 7.0 mW, using a laser beam with a wavelength of 784 nm and NA of 0.55, and its reproduction was evaluated at 0.9 m/s. There were obtained I11/Itop=0.52, I3/Itop=0.18, BLER 3000 cps or more and RF jitter of 45 ns or more for 3T. Thus, stable reproduction was difficult. Maximum reflectance Rtop of the signal after recording was 65%R. At that time, the average decomposition rate of the dye film was 7.1%.

INDUSTRIAL APPLICABILITY

[0076] The present invention can realize an optical information recording medium having a recording capacity two times or more higher than that of currently-used CD-Rs by using a material having optimum heat characteristics as an organic dye material of a recording layer without changing an outer diameter of the currently-used CR-Rs and can provide an optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs, which can comply with the high capacity for recording in order to deal with the increasing amount of data processing every year. 

1. An optical information recording medium having a recording layer formed on a transparent substrate having a spiral pregroove formed thereon, wherein: the pregroove has a track pitch Tp of 1.0 μm≦1.2 μm; and when it is assumed that the pregroove has a depth Dsub, the pregroove portion on the interface between the reflecting layer and the recording layer has a displacement depth Dabs, a real part of a complex index of refraction of the recording layer is nabs, a real part of a complex index of refraction of the transparent substrate is nsub, and a wavelength of reproduction light is λ, an optical phase difference ΔS 2Dsub{nsub-nabs(1−Dabs/Dsub)}/λ is 0.15≦ΔS≦0.55.
 2. The optical information recording medium according to claim 1, wherein a thickness Dg of the recording layer on the pregroove portion is 80 nm≦Dg≦120 nm.
 3. The optical information recording medium according to claim 1, wherein an optical distance difference ΔnDg between reflected light via the pregroove and reflected light via the land between the pregroove portions after recordation of information on the recording layer is 40 nm≦ΔnDg≦60 nm.
 4. (Amended) The optical information recording medium according to claim 1, wherein an imaginary part k of a complex refractive index of a recording layer is 0.1≦k≦0.25.
 5. (Amended) The optical information recording medium according to claim 1, wherein an average decomposition rate Ad of an organic dye material for the recording layer is Ad≦7.5%. 